1. Field of the Disclosure
This disclosure relates to energy storage and generation systems, e.g., combination of flow battery and hydrogen fuel cell, that exhibit operational stability in harsh environments, e.g., both charging and discharging reactions in a regenerative fuel cell in the presence of a halogen ion or a mixture of halogen ions. This disclosure also relates to energy storage and generation systems that are capable of conducting both hydrogen evolution reactions (HERS) and hydrogen oxidation reactions (HORS) in, the same system. This disclosure further relates to energy storage and generation systems having low cost, fast response time, and acceptable life and performance
2. Discussion of the Background Art
There are several technologies for energy storage and generation. These technologies can be divided into three subgroups: mechanical including pumped hydro, compressed air, fly wheels, and the like; electrical including super capacitors, super conducting magnets, and the like; and electrochemical including batteries, flow batteries, hydrogen storage, and the like. The current technology of electrochemical storage and generation is either expensive or inefficient or both. Generally, batteries can store and supply power at high efficiency, but are limited in capacity (total energy). Also, flow batteries are limited in power density and response time.
Fuel cells are often described as continuously operating batteries or as electrochemical engines. A typical fuel cell consists of two electrodes, an anode and a cathode, and a membrane interposed between the anode and cathode. Fuel cells operate by converting fuel combustion energy, such as hydrogen, to electrical power through an electrochemical process. It does so by harnessing the electrons released from controlled oxidation-reduction (redox) reactions occurring at the surface of a catalyst dispersed on the electrodes.
Regenerative fuel cells typically operate in harsh environments that can have an adverse effect on catalyst activity in the fuel cell. An important issue connected to catalyst activity in regenerative fuel cells that utilize, for example, a halogen acid electrolyte, is poisoning of the hydrogen catalyst by the halides. The membrane cannot completely prevent electrolyte crossover from one side of the cell to the other. For example, in a hydrogen tri-bromide fuel cell (HTBFC), bromides, e.g., tri-bromide, diffuse to the hydrogen electrode and poison the catalyst. Despite the fact that hydrogen oxidation/evolution reaction is fast and its overpotential is rather low compared to other voltage losses in the regenerative cell, in halogen ion-containing solutions, the catalyst is severely poisoned, and this raises the overpotential of the hydrogen electrode in the regenerative fuel cell.
Acceptance of energy storage and generation technologies depends on their cycle life and performance capability. In particular, with regard to regenerative fuel cells, they can be run, in addition to the direct mode, in the reversible mode, consuming electricity and the products of the direct reaction in order to produce the reactants of the direct reaction. For regenerative fuel cell such as hydrogen/bromine fuel cells, an important factor limiting its cycle life and efficiency is the degradation of the operating fuel cell materials. These materials are exposed to a highly corrosive bromine electrolyte for long periods of time at elevated temperature.
Energy storage and generation devices are needed for wide application with regenerative energy sources. Such storage and generation devices are useful in matching a varying energy supply to a varying energy demand.
A need exists for energy storage and generation systems that exhibit operational stability in harsh environments, e.g., both charging and discharging reactions in a regenerative fuel cell in the presence of a halogen ion or a mixture of halogen ions. Also, a need exists for energy storage and generation systems that are capable of conducting both hydrogen evolution reactions (HERs) and hydrogen oxidation reactions (HORs) in the same system. It would be desirable in the art to provide energy storage and generation systems having low cost, e.g., low cost electrolytes, fast response time, and acceptable life and performance.
The present disclosure provides many advantages, which shall become apparent as described below.